Hydraulic actuators, often referred to as hydraulic cylinders or hydraulic jacks, may be used for multiple applications. One typical application in which a hydraulic cylinder may be used is for lifting or lowering heavy loads such as bridges, structures, machinery, vehicles, rail cars, and large equipment. The loads may need to be raised for a variety of reasons such as performing maintenance on the load or repositioning the load. For most heavy loads, multiple hydraulic cylinders are employed to obtain the necessary amount of force and balance to lift the load.
Often, hydraulic cylinders are used not only as a lifting mechanism for these types of loads, but also as a support member once the loads are lifted. For example, a piece of heavy equipment may require maintenance and a technician may need to access the equipment from below in order to complete the necessary task. Once the equipment is lifted with the multiple hydraulic cylinders acting through hydraulic fluid under pressure, the hydraulic cylinders may also act as support members for holding up the heavy equipment. By using the hydraulic cylinders as support members, the technician may service the equipment from below.
Some mechanisms have been developed to provide a locking feature for the use of hydraulic cylinders as support members. One such mechanism includes using a lock nut to act as a stopping feature in the case of a loss of hydraulic pressure in the system due to a failure in one of the hydraulic cylinders, conduit for the hydraulic fluid, or the hydraulic pump. The lock nut may threadably engage a threaded portion of the plunger which axially extends from the piston of the hydraulic cylinder. When the plunger is raised by a supply of hydraulic fluid under pressure supplied to the hydraulic cylinder and the load has been lifted to the desired height, the lock nut may be turned down on the threaded plunger so that the lock nut is fixed relative to the hydraulic cylinder. In the event of a loss of hydraulic pressure to the system, the lock nut would prevent the plunger from retracting into the hydraulic cylinder, and thus, stops the load from lowering due to a loss of hydraulic pressure. Once the load no longer needs to be in the lifted position, personnel may then manually turn up the lock nut to the top of the plunger such that the lock nut does not prohibit the plunger from retracting into the hydraulic cylinder and the load may be lowered.
This system of manually turning a locknut, however, has several drawbacks. First, the hydraulic cylinder and load being lifted are not prevented from dropping due to a loss of hydraulic pressure until the lock nut is turned down by an individual. However, this task requires an individual to go below the load to turn down the lock nuts at the end of lifting, and to go back down to turn up the nuts before the load is capable of being lowered. Furthermore, the act of manually turning each lock nut may take a significant amount of time for an individual to perform in situations where multiple hydraulic cylinders are used to lift or lower a load.
Moreover, the load is at risk of damage while it is being lifted and lowered. Because the lock nut is not turned down on the plunger to prevent retraction of the plunger into the hydraulic cylinder until the load is lifted to its desired height, the load itself may be damaged if the hydraulic pressure is lost during the lifting process. Such a loss of pressure during the lifting of the load may result in the load being suddenly dropped from the hydraulic cylinder resulting in significant stress to the load. Similarly, because the lock nut is turned up to the top of the plunger to allow the plunger to retract into the hydraulic cylinder during the lowering process, a sudden loss of hydraulic pressure may result in the load being damaged as it is being lowered.
Even if the load does not fall from the support of a hydraulic cylinder during lifting or lowering of the load due to a loss of hydraulic pressure in one hydraulic cylinder, the load may still be damaged due to improper stress distributions resulting from a loss of support by that cylinder. For example, when a load is lifted or lowered by multiple hydraulic cylinders and hydraulic pressure fails in just one of the hydraulic cylinders, the load will still be supported by the remaining properly functioning hydraulic cylinders. Thus, the load will not be subject to damage from suddenly dropping, as in the case where hydraulic pressure is lost to multiple hydraulic cylinders. However, by not having adequate support on the load due to a loss of a support member, the load may still be damaged due to uneven stress distributions.
In fact, heavy loads that must be lifted with multiple hydraulic cylinders often need to be lifted by the hydraulic cylinders in a synchronous manner to avoid applying uneven stress to points of the load during lifting or lowering. To prevent such uneven stress on the load, synchronous lifting may need to be very precise to ensure that the hydraulic cylinders are not raising or lowering at different rates introducing undesired flexing in the load, as well as to ensure that appropriate balance is maintained on the load.
Consequently, a need exists for a hydraulic cylinder position sensing and locking system that allows for loads to be lifted, lowered, and supported in such a manner that avoids the disadvantages previously discussed.